Friction clutch



Feb. 27, 1940.

G. CARWARDINE 2,191,846

FRICTION CLUTCH Filed June 22, 1937 5 Sheets-Sheet 1 20 Fig.1.

11 14 12 f g a 17 is I lNVE/VfOR q C 4/1 vv/r/ap/n/g Feb. 27, 1940. G.CARWARDINE FRIc'rIoK CLUTCH Filed June 22. 1937 5 Sheets-Sheet 2 //VVE/V 70/? 4Cwmyygpava I 14 7'7 DRIVE )5 Feb. 27, 1940. G. CARWARDINE2,191,346

I FRICTION CLUTCH Filed June 22, 1937 5 Sheets-Sheet 3 Fig. 3.

7 1940. e. CARWARDINE 1 8 5 FRICTION CLUTCH Filed June 22, 1937 5 sheetssheet 4 4e piazza/M5 BY Feb. 27, 1940. c w Rm E. 2,191,846

FRICTION CLUTCH Filed June 22, 1937 5 Sheets-Sheet 5 A TT R/VE PatentedFeb. 27, 1940 FRICTION CLUTCH George Carwardine, Bath, EnglandApplication June 22,

1937, Serial No. 149,788

In Great Britain June 25, 1936 9 Claims.

This invention relates to friction clutches. Such devices are mostcommonly used for transmitting rotary motion from a driving shaft orother member to a driven shaft, but friction clutches are also used asbrakes for retarding angular motion, in which case a rotary member and astationary member have to be brought into engagement. The invention isconcerned with friction clutches of all kinds, and in particular, isapplicable to clutches acting as brakes both for bringing machinery torest and for maintaining a rotating member at a regulated speed, as isrequired frequently in speed regulating devices. 1 l

A One important application of the invention is to friction clutches ofwhich thesurfaces are brought into-operative engagement by means ofcentrifugal force. Such clutches have been proposed for automaticallyengaging the transmission gear of motor vehicles upon the drivingmember'attaining a predetermined speed. Centriiugally operated clutcheshave been suggested in which revolving masses in the .form of expandingshoes lined with friction material are pressed into operative engagementwithin a surface of a cylinder ordrum by. centrifugal force; however,these clutches are in fact impracticable when designed to engage at suchcomparatively low speeds, within the range of so small a change,

of speed, as is generally desirable in motor vehicles and the like,because of the enormous excessof centrifugal force which in that casewould be generated at higher velocities. i

The present invention, therefore, aims at providing a form of frictionclutch in which the force required to be exerted for operating theclutch, whether that force is a centrifugal force or exerted by theoperator is so considerably reduced that it need not be greater thanthat necessary to overcome friction, and in the case of centrifugalclutches the engagement can be effected at as low a speed and withinassmall a range of velocity change as desired. According to the presentinvention, a friction clutch is furnished with an operating mechanismwhich includes two elastic force units. One of these units, which willbe called the first unit, serves primarily as a resilience and isinserted between an engaging part of the clutch and a member or membersby which the engaging force is applied and actually this unit isseparate from and additionalto the resilience which may reside in theparts of the mechanism for transmitting the forces for operatingthezclutch. The other elasticf orce unit, which will be called thesecond unit, comprises a mechanism by means of which the falling forcecharacteristicof a relaxing spring or the like is converted into a risinforce effort and the said mechanism is so arranged that it may be set ina position inwhich it is rendered capable of storing energy in the firstelastic force unit and in doing so it can supply a force required tomaintain the engaging parts of the clutch in operative engagement.

The first unit may conveniently be constituted by a number of helicalcompression springs which are compressed by the second unit when thelatter is rendered active. The second unit, as allready i'ndicated, mayconsist of any form of mechanism which converts the falling forcecharacteristic of a relaxing spring or the like into a rising forceeffort. In its simplest form, however, the second unit comprises one; ormore levers or struts associated with one or more springs, the levers oreach lever being mounted so as to rock to and from a dead centreposition with respect to the line of action of its respective springs,:and the springs being arranged so that a transverse component of theforceexerted by the springs is available for opposing that exerted bythe first unit.-

The two elastic force units may be made exactly or nearly to balance oneanother throughout the efiective range of movement of the mechanismsothat apart from the effort required to overcome friction, no additionalforce or only a small force is needed toputthe clutch either in or outof engagement. When the clutch'is arranged as a centrifugal clutch, thefirst elastic force unit is given a higher rate'than the rate of thesecond elastic force unit and energyjis only stored in the'first unitwhen the force exerted by the second is supplemented by, the centrifugalforce exerted by one or more massesrotated with the driving member ofthe clutch so that the latter is automatically brought into engagementupon the driving member attaining a predetermined speed. When the firstmember comprises a number of springs it is the combined rate of allthese springs which comes into question and when this combined rate ismade a little greater than that of the second unit which may comprise anumber of extension springs, the resistance intended to be overcome bythe centrifugal force exerted by the rotating masses may be provided byadditional springs to the compression springs referred to but, yetforming part of the first elastic force unit. These additional springsmay act between anengaging part of the clutch and a fixed part ofthehousing so that when the rotating masses begin to exert force, theclutch parts are movedinto engagement and the additional springs arequickly compressed to their full extent and thereupon the force exertedby them remains constant. This latter arrangement has the furtheradvantage that the additional springs may be made toserve a furtheruseful purpose, that isto say, they may keep the engaging part of theclutch quite free of the driven part when the clutch is disengaged.

The invention lends itself to various neat and compact forms ofconstruction. The first elastic: force unit may consist of a number ofhelical compression springs arranged to exert their pressure directly ona member which. forces the clutch members into engagement and between afloating plate or similar member on which the second elastic memberdirectly exerts its force. In such a case there are no linkages orjoints,.

or practically none, in the mechanism transmitting the force to bringthe clutch into engage-- men-t, and therefore, no inherent resilience inthis mechanism. The secondelastic force unit, as already indicated, maycomprise a number of springs which are stressed in a dead centreposition when the clutch is-disengaged. The first elastic force unit, inserving as a. resilience, is necessary to enable the springs of thesecond unit to be moved from. their dead centre positions, and the totalforce exerted by the second unit is resiliently transmitted through thecompression springs to the clutch engaging parts.

In order that the invention may be more clearly understood and readilycarried into effect; several forms of construction inaccordancetherewith will now be described by way of example with reference to theaccompanying drawings, in which: I

Figure 1 is a central longitudinal section of a form of centrifugal orautomatic clutch suitable for use on a motor vehicle;

Fig 2 is an elevation seenfrom the right in Figure 1 with the casingpartly removed in the upper half;

Figure .3 is a view similar to Figure 1 showing a manually-operatedclutch suitable for driving machine tools, the parts being shown in'thedisengaged position;

Figure 4 is a view corresponding to the upper part-of Figure 3 with theparts in the engaged position;

Figure 5 is an elevation from the right of Figure 3 similar to thatshown in Figure 2; and

Figure 6 is a section similar to Figure 1 of the upper part of a clutchof slightly modified construction.

Referring to Figures 1 and 2, a cylindrical casing 6 is secured at itsflanged open end to the enginefly wheel 2 so as. to run coaxially withthe latter. Around the inner surface of the cylindrical part 'of thecase I are a number of guide pins 3 screwed into the fly wheel 2. Thesepins 3 serve to guide a pair of discs or plates 4, 5 arranged to slidewithin the casing l with their faces substantially parallel to the faceof the fly wheel 2. Between the disc 5 and the face of the fly wheel isinterposed a third disc or plate 6 which is in fact the driven plate ofthe clutch and is'keyed to the driven shaft 7, the bearing of which isnot shown. In the case of a motor vehicle, however, the shaft 1 would bethe input shaft to the gear box of the vehicle. The plate 6 is faced onboth sides with friction material 8, arranged to come into contactrespec- 2,191,846 v tively with the face of the fly Wheel 2 1 and theplate 4.

A number of helical compression springs Q are i:

interposed between the plates t and 5. In the examples shown there aresix such springs 9, and

as seen in Figure 1 the total length of the clutch. y is reduced byhousing the right hand ends of the.

springs -9 in shells or ferrules Hl secured in the plate 5. The springs,9 aredesigned so that a combined force exerted by them, when properlycompressed by a movement of the plate 5 to the left, is sufficient toprovide the necessary driving torque on the driven plate 6, so that thesprings: 9 constitute the first elastic force unit already referred to.

The plate 5' is provided with three lugs H distributed equidistantlyaround the plate and' serving as bearings for the pivots of three bellcrank levers l2. engagedposition, as shown in Figure 1, the compressionsprings 9 being then just free, it will be seen that onev arm [-3. ofeach. bell crank: lever i2 is directed towards the. axis of. the clutch,

while the other arm M is directed parallel to the shaft T away from theplate 5.". The arm I3 of When the parts are in the dis eac'h'bell crankis provided with a. pair of freely 7 mounted rollers I5 adaptedtoremain. in contact 3 with a bearing. ring it fixed in the outer plate 1of" the casing I. The free, end of the. other arms 14 of the bell.cranks each bear a suitable mass l l for providing the necessarycentrifugal force. The pin l8 which. forms the journal of the bearing ofthe free mounting of the rollers 15 is extended in both directions.beyond the face ofqits bell crank lever l2, asseen in Figurev 2, andthese ends serve as one anchoring point for each of a. pair of stressedhelical extension springs, 19 which, at their other or outer ends, are.anchored to similarly spaced projections. 20 carried from thecylindrical part of the casing I.

The pins i8 and 2.0. are so located axially of the shaft 1,

that. the axesrof the springs I9 are'parallel to the face of theflywheel 2 and the springs I 9 are fully extended'i'n the dead. centreposition v shown in Figure 1 when the springs 9. arev just free, In thatposition, also, the freely mounted rollers l5 are only just in contactwith the. face of the bearing ring 16.

Thus, in. the particular form shown in Figures 1 and2, the essentialelement of the secondclastic force unit are the pairs of stressedextensionj springs l9 and the inwardly directed arms i3 of thebell'crank-levers l2, and it will be seen' that while the lovers ['2 arein-equilibrium with respect to the force of the. springs I9 in thewholly disengaged position of the clutch shown in Figure 1, thatequilibrium is: unstable and any outward movement of the. arms i4 due tocentrifugal force will cause the pivots of the bell cranks l2 to move tothe left in Figure 1,- so that immediately the. springs Hi exert anincreasing counter-clockwise moment on the bell cranks I2,

. which, when added to that exerted by the centrifugal force will, owingto the reaction of the rollers !5 present on the ring it, force theplate 5 to move to the. left in Figure 1 against the in-'vcreasing'resistance of the springs =9, and in this way effect engagementof the clutch.

It may be mentioned that, in this case, the springs 9 and the springs Itmay be arranged to be balanced or substantially balanced in allpositions over therange of movement and when no centrifugal force isexerted, it is arranged for further compression springs 2! to maintainthe 1 plate 4 clear of the driven plate 6. The springs vv part-o1 theplate 5. As soon as the plate ,5 is

position or disengaged position shown in Figure l, the springs I9 haveno effective action and it is the pressure exerted by the springs 2|alone which determines at what centrifugal force the springs [9 can bemoved off the dead centre position.

It should also be noticed that since the bearing ring l6 is fixed in thecasing I, the pivots of the rollers l5 never move with respect to thecasing and as the anchoring pins are also ,carried from the casing I itfollows that the axes of the springs 19 remain parallel to the face ofthe fly wheel 2 in all positions of the mechanism so that in this formof construction the force exerted to overcome the resistance of thecompression springs 9 is not only a transverse component of the forceexerted by the extension springs I 9, but in actual fact, in this caseit is a right angular component. When this particular relation existsbetween the force of the relaxing springs l9 and the transversecomponent, it is a fact that by designing the springs I9 so that theirmaximum' extension is substantially equal to the length of the strut orlever l3' of the system, that is to say, so that if the bell crank 12were turned through a right angle, the spring l9 would be completelyrelaxed, the right angular component is then of exactly the proper orderrequired for overcoming the resistance of the springs 9 whether they arecompression springs, as shown, orextension springs.

For the reasons already given. the rate of the springs 9, together withthe springs 2|, is made a little greater than that of the springs i 9,the difference depending upon the speed at which it is desired thecentrifugal masses I! shall cause engagement of the clutch, but it ispossible to make the rates of both elastic force units the samethroughout their range, and indeed, a clutch designed on that principleis shown in Figures 3 to 5.

. In these figures the casing l corresponds to the casing l inFigures land 2, and the driving member 2, on which a spur wheel 22 is mounted.corresponds to the fly wheel 2 in Figures 1 and 2. Inthis case theclutchis intended for use with a machine tool, so that the driven shaftI carries a spur wheel '23 which may form the first member of thegearing. say, of a lathe, the plates 4, 5 corresponding. exactly to thecorresponding parts in the previous construction as do the driven clutchplate 6 and the friction material 8. ,The springs 9 likewise bearbetween the plates 4 and the ferrules 10 carried by the plate 5. Theplates 4 and 5 are also guided on pins 3. The second elastic force unit,however, is slightlv differently arranged in this case. The levers I2are pivoted at 24 to the cas ng 1 instead of to the plate' 5, and sincethe lower end of the springs l9 are now anchored to the pivots of therollers 15 which move to the left with the plate 5, the pins 29 formingthe upper anchor for the springs l9 are also carried from the plate 5 sothat again the axes of the springs i9 remain parallel to the face of thedriving member 2 over -mass'3l on an extension of the lever l2.

moved slightly to the left the lower end of the lever 12 is movedslightly to the left and the springs l9 are enabled to exert clockwisemoment on these levers and to apply the clutch in a manner similar tothat described with reference to Figures 1 and 2.

In this case, as already indicated, it is assumed that the springs 9 areexactly balanced by the springs IS in all positions of the mechanism, sothat all the operator has to do is to overcome friction in the partswhereupon the springs I9 immediately come into play and the.

full force exerted by them is utilised in maintaining the clutch platesin engagement.

In this form of construction-the operator positively withdraws theclutch when desired. In the form of construction shown in Figures 1 and2, the clutch is withdrawn automatically on the speed falling to apredetermined amount but it may be desirable to provide means enablingthe operator to disengage the clutch, even if the speed is too high forthis to happen automatically. To provide for this, small pull rods 26are screwed into the plate d and heads 21 on these rods may be engagedby levers 28 the casing at the point la, when the plate 5 is still wellclear of the plate 4.

In the constructions shown in Figures 3 to 5. since the lever l2 and itspivot is set off the centre of the shaft 1 it would exert a certainoutward centrifugal force at speed but this force can be balanced bythat of a counterbalancing It is evident, however, that this state ofbalance can only exist in one angular position of the lever l2, sincewhen the lever l2 rocks, the mass 3!. moves nearer the shaft 1 and themass at the lower end of the lever 12 moves further away so that thecentrifugal force would be out of balance and tend to cause furtherrocking of the lever l2 in a clockwise direction and assist in the fullengagement of the clutch. Similarly. if the operatorin disengaging theclutch passes over the balanced position, then it is clear that theforce exerted by the mass 3! is then greater than that exerted by thelower end of the lever I2 and the unbalanced centrifugal force will movethe lever l2 still more counter-clockwise and complete the disengagementof the clutch. In Figure 6, a form of construction similar to that inFigure l is illustrated and corresponding reference numerals have beenemployed. In this case, however, the arrangement of bell crank leversand extension springs is replaced by an equivalent arrangement ofcompression springs and telescoping struts. The springs in this caseare-compression springs l9a, and they bear between an outer sleevemember 32 and an inner member 33 which telescopes within'the member 32so as to tend to separate them. The outer member 32 terminates at thelower end in a head 34 with a hardened plane lower surface bearing on apin 35 mounted in an extension of the casing I. Similarly-the innermember 33 terminates at its upper end in a similar head 36 with a planeupper face bearing against a pin 3'! which, howranged that the arms 12come into contact with 5 ever, is, mounted in an. extensionBB of theplate 5.

The lever l2 and mass l1 form an extension of,

the outer member 32.

In the position shown in Figure 6, which is the when there is sufiicientcentrifugal force to rock the lever l2 and the member 32 which carriesit,

the pin 31 is moved slightly, to the left and the thrust of the springIlla commences to have an increasing component directed to the left andtending to press the plate 5 to the left, with the result that thesprings 9. are compressed and the clutch engaged as in connection withFigure l.

The invention can be applied in the form of a centrifugal clutch fordriving machinery and then incorporated in the design of the. drivingpulleys. For example, a pulley so constructed could be driven by asynchronous electric motor and would run free of its shaft, with theclutch disengaged, until the speed approached the synchronous speed ofthe motor when the clutch would be engaged by centrifugal force and theload would be driven. This enables a synchronous motor to be run up tospeed light. and then to take up the load.

I claim:

1. A friction clutch comprising in combination, frictionally-engagingparts, a movablymounted member for transmitting engaging force to saidparts, a first elastic force unit interposed between said member and oneof said frictionallyengaging parts, a second elastic force unit havingalower rate than said first elastic force unit and comprisinga convertermechanism organized to convert the falling force characteristic of .arelaxing elastic member into a rising force efiort and in operativeconnection withsaid movablymounted member, and centrifugal means forsupplementing the action of said converter mechanism and for renderingsame operative, upon said movably-mounted member to take part, in con--junctionwith said centrifugal means, in storing energy in said firstelastic force unit and so to bring said frictionally-engaging parts intoengagement at a predetermined speed of rotation.

2. A friction clutch comprising in combination, frictionally-engagingparts, a movably-mounted member for transmitting engaging force to saidparts, a first elastic force unit interposed between said member and oneof said frictionallyengaging parts, a second elastic force unit havingsubstantially the same rate as said first elastic force unit andcomprising a converter mechanism organized to convert the falling forcecharacteristic of a relaxing elastic member into a rising force effortand in operative connection with said movably-mounted member and meansfor rendering said converter mechanism operative upon saidmovably-mounted member to take part in storing energy in said firstelastic force unit and so to bring said frictionally-engaging parts inengagement.

3. A friction clutch comprising in combination, frictionally-engagingparts, a movably-rnounted member for transmitting engaging force to saidparts, and a first. elastic force unit interposed between said memberand one of said frictionallyengaging parts, and a second elastic forceunit comprising a converter mechanism organized .to convert the fallingforce characteristic of a relaxing elastic member into a rising forceeffort and in operative connection with said movablymounted member, saidsecond elastic force unit substantially balancing said first elasticforce unit throughout the range of movementso that only the force.necessary to overcome: friction: is

required to engage or disengage the,- clutch.

4; A friction clutch comprising in combination, frictionally-engagingparts, a, movably mounted member for transmitting engaging. force tosaid parts, a first elastic forceunit interposed dead centre position, atransverse component-of I the force exertedby said spring is. applied'tOiO rpose that exerted by saidfirst elastic force unit;

and a rotatably mountedrnass operatively con nected with said lever torock the latter fromlits, dead centre positionby centrifugalv force andso. to render said spring effective at a predetermined speed ofrotation. Y

5. A friction clutch comprising in combina.-- tion, a driving element,a. driven element,'a mov ably-mounted plate for transmitting engaging,

force toone of said elements, a plurality, of compression springsinterposed between said plate and the said one of said elements, aplurality of levers each fulcrumed in said movably-mounted plate, aplurality of extensionsprings each an-- chored to one of said levers andto'a fixed anchor point, each of said levers being mounted torock,

to and from a dead centre position with respect to the line of action ofits associated springand,

means for moving said levers from their dead.

centre positions to enable said extension springs to exert a transversecomponent of their force upon said movably-mounted plate to oppose the.

force exerted by said compression springs and to effect frictionalengagement of said driving and driven elements.

6. A friction clutchv comprising in combination, a driving element, adriven element, a movl-v ably-mounted plate for transmitting engagingforce to one of said elements, a plurality of comand the said one ofsaid elements, a plurality of levers each-fulcrumed insaidmovably-mounted plate, a plurality of extension springseac-hanchored to one of said levers and to a fixed an,-

. pression sprlngs interposed between. said plate i chor point, each ofsaid levers being mounted to rock to and from a dead centrepositionwitl'irespect to the line of action of its associated. spring, J

and a rotatably-mounted mass, attached to-each of said levers so as tomove said lever from its dead centre position due to centrifugal force,at. a predetermined speed of rotation to enable each of said extensionsprings to exert atransverse component of its force upon saidmovablymounted plate to oppose the force exerted 'bysaid compressionsprings and to efiect frictionalengagement of said driving and drivenelements.

7. A friction clutch, comprising in combination, a driven element, adriving element slidably mounted to move into engagement with saiddriven element, a niovably-mounted plate for' transmitting engagingforce to said slidablymounted driving element, a plurality of springsinterposed directly between said vmovablymounted plate and saidslidably-mounted driving element and unstressed in the disengagedposition of theclutch, a second elastic force unit comprising aconverter mechanism organized to convert the falling forcecharacteristic of a plurality of relaxing springs into arising force761" effort exerted directly upon said movablymounted plate during'theclutch-engaging movement and when theclutch is engaged, and means forrendering said converter mechanism operative on said movably mountedplate to take part in storing energy insaid plurality of springs and soto maintain said driven and driving elements in engagement.

8. A friction clutch comprising in combination, frictionally-engagingparts, a movablymounted member for transmitting engaging force to saidparts, a first elastic force unit comprising a spring interposeddirectly between said member and one of said frictionally-engagingparts, and unstressed in the disengaged position of the clutch, vasecond elastic force unit comprising a spring and a lever mounted so asto rock to and from a dead centre position with respect to the line ofaction of said second-mentioned spring, said second-mentioned springexerting through said lever a force on said movably-mounted member in adirection perpendicular to the line of action of said second-mentionedspring, and being entirely relaxed when its effective lever arm isperpendicular to its line of action, and a rotatably-mounted massconnected to said lever so asto rock said lever from its dead centreposition at a predetermined speed of rotation in order to exert a thruston said movably-mounted member and to enable said second-mentionedspring to act in conjunction with said thrust to bring saidfrictional-engaging parts into engagement.

9. A friction clutch comprising in combina-' tion a member mounted torotate about an axis, a second member mounted to rotate about said axisand to move along said axis to engage said first-mentioned memberfrictionally with pressure increasing from zero, a third member mountedto rotate with said second member and to move relatively thereto alongsaid axis, a first elastic force unit interposed between said second andthird members, and a second elastic force unit mounted to rotate withsaid third member and comprising a spring and a lever mounted to rocksubstantially to and from a dead center position with respec-tlto theline of action of said spring, the latter being arranged so that, whensaid lever is rocked away from said dead center position, said springrelaxes while exerting an increasing transverse component of force onsaid third member to increase the pressure between said first-mentionedand second members by stressing said first elastic force unit, and that,

when said lever is substantially in said dead center position, saidfirst elastic force unit is relaxed.

GEORGE CARWARDINE.

